1. Field of the Invention
The present invention relates to secure data systems having cryptographic keys for encyphering and decyphering data. More particularly the present invention relates to apparatus and methods for altering the cryptographic keys used to encypher and decypher electronic data.
2. The Prior Art
Electronic cryptographic systems are well known. Such systems are used in the encyphering and decyphering of communications, and are also used to encypher and decypher other electronic data which must be transmitted between and among computers and data processing equipment and systems for various purposes when the security of transmitted data is an important consideration. Such applications include banking operations, such as automated teller machines and wire transfer communications, as well as many other important business communications.
Cryptographic systems utilize a master key or keys, which are used in one of several known algorithms to both encrypt and decrypt data. Such keys are usually resident in a control portion of the system. Since the security and integrity of any cryptographic system is dependent on the security of the keys utilized in the system, good practice dictates changing cryptographic master keys every so often to minimize the likelihood that unauthorized persons may be able to "break" the encryption and thus either have access to the data, or have the ability to alter data and create false data.
In a typical secure data processing system, an application presents to the cryptographic device a unique key which has been encrypted by use of a master key resident in a cryptographic device associated with the system, and some data to be encrypted or decrypted. After decryption, if the key is recognized as valid, the application is allowed to gain access to the cryptographic device. The data is appropriately manipulated and the key is re-encrypted using the master key. The data and the re-encrypted key are then returned to the application.
In all prior art cryptographic systems known to the inventors, any master key changes are made by gaining access to the place where the master key is stored, using whatever security measures which have been designed into the system to assure its security, and substituting the new key for the old key. In systems which have distributed keys among a plurality of applications, the key change must be communicated to all system nodes which have a need for local storage and use of a key.
A problem arises, however, in such distributed systems when a given application to which a new master key has not been communicated attempts to communicate with the cryptographic device or other portions of the system. Conventional systems have no provision for recognizing the superceded key as valid and will thus not allow its use. Thus, the application which has not received the update will not be able to handle encrypted communications with the rest of the system until it has received the new key.
The potential problem increases in importance as the use of widely-distributed information networks becomes more prevalent, and, concurrently, as the speed and frequency of encrypted data communications also increases. It is apparent that it would be desirable to provide for recognition of superceded cryptographic keys in distributed cryptographic data systems until they can be changed.